This invention relates generally to vibration monitoring instrumentation for fluid compressors and more particularly to an instrument for monitoring compressor vibration to detect and record compressor surging. This invention is a result of a contract with the United States Department of Energy.
In fluid-processing systems, such as a gaseous diffusion system for separating isotopes, which require a larger number of rotating, constant flow compressors, such as axial flow or centrifugal type for flow control, the compressors are designed to operate under certain well-defined stable flow conditions. When the flow becomes unstable due to shutdown of a stage in the system, plugging of a stage, various scheduled changes in flow conditions, or other flow disturbing problems in such a system, compressors in the system will surge. Compressor surge may be defined as a large amplitude, low-frequency oscillation of the total annulus-averaged flow through the compressor. Each time a compressor surges the compressor blades and seals are subjected to very high stresses. Excessive surging may eventually weaken the compressor blades to a point that deblading is possible.
Therefore, these compressors are designed to withstand a limited number of surges over an estimated life span. However, the actual number of surges a compressor may experience in a selected period is not known. In a diffusion cascade, for example, the only method for counting compressor surges involves human interpretation of flow parameters. Therefore, in order to obtain a definite record as to the frequency and total number of times a compressor experiences surging during operation, there is a need for instrumentation to count surges in constant flow-type compressors to aid in scheduling compressor blade and seal maintenance or predict life expectancy of a compressor in a given system.